Add first-class support for Date-Time values for JSON-API

[tatu-at-datastax]

Currently we support a subset of datatypes Mongoose supports, basically matching native JSON types (Objects/sub-docs, Arrays, Number, Strings, Booleans, null), and one pseudo-type (Doc Id).

It would make sense to also support Date/Time, so users need not handle conversion to/from JSON String or Number types, but can use native Javascript Date type (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date) on client-side and get it efficiently handled on JSON API server side.

Current thinking is to convention defined by EJSON (https://docs.meteor.com/api/ejson.html), in which numeric (milliseconds since 1.1.1970 timestamp, standard used by Java and Javascript as well as many other platforms) is encapsulates as a single-entry JSON Object like:

{ "$date": 1358205756553 }

This allows for reliable auto-detection because JSON API Object/sub-doc properties can not start with $ character.

Details of this approach will be added here and after/during prototyping Spec needs to be updated. We will also file separate issues for different parts of handling; so tasks include:

• Update Spec to describe storage and logic
• Create new index field for Date/Time values, update hashing, shredder ((Date/Time support) Add DB column query_timestamp_values, Shredding support #370)
• Change Insert and Update operation to update timestamp index column ((Date/Time support) Change Insert and Update operation #378)
• Change doc-id (_id) handling to recognize and support new id type ((Date/Time support) allow use of Date/Time as Document Id (_id) #371)
• Test that (and change if need be) update operators work with Date/Time values ((Date/Time support) Allow update operators on Date/Time valued fields #372)
• Test that (and change if necessary) Projection works with Date/Time values ((Date/Time support) Ensure Projection of Date/Time valued fields works #373)
• Change in-memory sort to auto-detect and convert Date/Time values appropriately for sorting ((Date/Time support) Support sorting on Date/Time valued fields #374)
• Change query filters to auto-detect and convert Date/Time values appropriately for equality queries ((Date/Time support) Support full filtering on Date/Time valued fields #375)
• Add support for $currentDate update operation ((Date/Time support) Add $currentDate update operation #397)

[vkarpov15]

Just a couple of details to confirm:

1. Mongoose only has one Date type that corresponds to a Date in JavaScript and a Date in MongoDB. Mongoose doesn't have first class support for MongoDB's internal timestamp type.
2. Mongoose does not expect timezone information to be stored with the date. Dates are 64 bit ints in MongoDB.
3. There are no special query operators for dates. However, $eq, $in, $lt, $lte, $gt, and $gte all work on dates. In particular, myDate: { $gt: new Date() } gives you all documents where the myDate property is after right now.
4. There is one special update operator for dates: $currentDate. That sets a property to the current date. In my experience, $currentDate is rarely used because it is easy to simply set a date to the current date.

[tatu-at-datastax]

@vkarpov15 Excellent -- thank you confirming. This aligns with our understanding of things, plans (only supporting Date, not Timestamp; storage as 64-bit milliseconds since epoch; no special operators aside from $currentDate (which may be added but is not super popular)).

[tatu-at-datastax]

All sub-tasks completed, Date-Time type support considered complete.